1. Field of the Invention
The present invention relates to a method of measuring characteristics of a semiconductor element and a method of manufacturing a semiconductor device using the same.
2. Description of the Background Art
In the steps of manufacturing for semiconductor chips constituting a semiconductor device, a so-called wafer test is conducted in which a conduction test for semiconductor elements formed on a semiconductor wafer (hereinafter, also simply referred to as a “wafer”) is conducted in a wafer state. In some cases, electrodes of a semiconductor element are formed not only on one side in a wafer thickness direction (hereinafter, also referred to as a “front surface side”) but also on the other side of the wafer thickness direction (hereinafter, also referred to as a “back surface side”). In a conventional wafer test, the back surface side of the wafer is stuck fast to a conductive wafer stage. In order to render the electrode on the back surface side (hereinafter, also referred to as a “back surface electrode”) conductive, the back surface electrode is rendered conductive through the wafer stage used as an electrode.
For example, in a case of a wafer on which a power metal oxide semiconductor field effect transistor (MOSFET) is formed (hereinafter, also referred to as a “power MOSFET wafer”) as a semiconductor element, a drain electrode is formed on the back surface side and a gate electrode and a source electrode are formed on the front surface side. Therefore, the back surface side of the wafer is stuck fast to the wafer stage to electrically connect the drain electrode on the back surface side to the wafer stage, and the gate electrode and the source electrode on the front surface side are brought into contact with a probe terminal, to thereby secure an application electrode in the wafer test.
In order to achieve higher performance of a semiconductor device, development has been made to slim down a wafer. A slim wafer reduces the resistance between a drain and a source, which reduces conduction loss.
In a case where a wafer is slimmed down, the wafer is likely to be warped, which makes handling thereof difficult. For example, a wafer test is conducted on the warped wafer in a state of single wafer (hereinafter, referred to as a “state of bare wafer”), the wafer is damaged, for example, is cracked or broken. Therefore, a wafer test cannot be conducted in a state of bare wafer. In order to conduct a wafer test, the wafer needs to be supported by attaching a dedicated sheet or an insulating substrate to the back surface of the wafer.
In a case where the wafer is supported by attaching a dedicated sheet or the like to the back surface of the wafer, the wafer is insulated from the wafer stage even if the wafer is stuck fast to the wafer stage. This leads to a problem that an electrode on a back surface side of the wafer, for example, in a case of a power MOSFET wafer, a drain electrode of a power MOSFET cannot be rendered conductive.
To solve the above-mentioned problem, there is used a method of conducting a wafer test with a specific electrode formed on the front surface side of the wafer as a drain electrode or a method of conducting a wafer test with a source electrode formed on a front surface side of an adjacent chip as a drain electrode (for example, see Japanese Patent Application Laid-Open No. H08-153763).
However, in the conventional method disclosed in, for example, Japanese Patent Application Laid-Open No. H08-153763, a wafer test is conducted by bringing an electrode formed on a front surface side of a wafer into conduction and applying a voltage between the electrode and a source electrode, and thus a depletion layer from the source side fails to extend sufficiently toward a drain side that is the back surface side of the wafer. Accordingly, electrical characteristics of a semiconductor element cannot be measured with accuracy. For example, while an initial channel leakage current can be measured with accuracy, the leakage current under application of high voltage cannot be measured accurately.